This application claims the priority of German Patent Document 100 35 333.9, filed in Germany, Jul. 20, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a rotor blade for a helicopter having an aerodynamic control flap, particularly a camber flap, which is integrated essentially in the contour of the blade profile, is swivellably arranged on an axis of rotation and to which a control device, particularly a control rod, is linked outside the axis of rotation, for converting a linear movement into a swivelling movement of the control surface.
In comparison to conventional airplanes, helicopters have many advantages. The vertical starting and landing permits a maneuvering in locally limited areas. As a result of the ability to fly at a low speed, the helicopter can be used for monitoring tasks. The possibility of hovering predestines the helicopter as an operating device for rescue missions.
The vertical lift and propulsion is caused by the rotation of the rotor blades about the rotor mast in that the rotor blades generate a lift which is directed according to the position with respect to the rotor mast. The position of the rotor blades and thus the lift and the propulsion of the helicopter are normally ensured by the rotating of the rotor blades along an axis in the span direction by means of a wobble plate and a linkage of bars situated between the latter and the rotor blade. As an alternative, it is possible to influence the position of the rotor blades by way of control flaps. A swivelling of the control flaps results in a change of the approach flow behavior of the air.
In this case, servo flaps can be used as control flaps on the trailing edge of the profile in order to reduce the typical knocking noise of the rotor blades. This is caused by the interaction between the rotor blades and air vortices which are shed from the preceding rotor blade. Servo flaps are used in this area in order to reduce the aerodynamics of the interaction in that the vortices are diminished by a slight setting and attraction and are repulsed further toward the outside.
As a result of a lifting and lowering of a control flap mounted as a camber flap on the leading edge of the profile, the high suction peaks are reduced on the leading edge of the profile when the rotor blade is in a reverse motion, whereby the flow shedding is delayed in this phase and the hysteresis loops are reduced in the course of the aerodynamic coefficients. In addition, a discrete camber flap on the leading edge of the profile permits that the energy required in the case of a continuous contour variation for the elastic deformation be used for overcoming the aerodynamic forces and moments or that a greater authority of movement be provided.
From T. Lorkowski, P. Jxc3xa4nker, F. Hermle, S. Storm, M. Christmann, xe2x80x9cConcept Development of a Piezoactuator-Driven Leading Edge Flap for the Dynamic-Stall Decelerationxe2x80x9d Annual Conference of the DGLR, Sep. 27-30, 1999, a camber flap on the leading edge of the profile is known in the case of which the force of a piezoactuator is transferred by way of a forcing lever to a flap linking point. This linking point is situated above the axis of rotation of the camber flap, so that, by way of the lever arrangement, the flap is swivelled downward when the forcing lever is moved forward and is swivelled upward when the forcing lever is moved backward. According to the lever arm (distance between the flap linking point and the axis of rotation) and the path of the forcing lever, different displacements can therefore be achieved.
The problem of this type of an arrangement is the fact that, in the case of a simple mounting of the forcing lever at the flap linking point, because of the centrifugal forces of up to 1,000 g occurring during the operation and because of the load in the forcing lever, a tilting of a bearing will occur which will result in a limited operation. During one rotor rotation, the camber flap is moved back and forth several times, so that under the high loads, a wear of the components occurs in the case of a simple mounting. In addition to an increased energy input for the movement of the flap, this has the result that a tilting can occur even more rapidly because of the resulting increased play of the mounting.
It is therefore an object of the invention to provide a rotor blade having an aerodynamic control flap, in the case of which the flap can be controlled at high regulating speeds during the operation at a centrifugal force load of up to 1,000 g by means of a control device, without the occurrence of a tilting of the control device and of the control surface. For a low-maintenance design, the wear of the individual components should also be low.
For achieving this object, a rotor blade of the initially mentioned type according to the invention is characterized in that the control device is supported by way of roller bearings and bolts aligned in the span direction, and devices are provided which absorb by way of the control flap centrifugal forces of the control device, which result from the rotation of the rotor blade.
Because of the transmission of the kinetic energy of the control device to bolts which are supported by means of roller bearings, the risk of a tilting is lower than in the case of a simple point mounting. In addition, the centrifugal forces are absorbed by way of devices of the control flap so that, even in the event of different centrifugal force loads, a stable controlling of the control flap is ensured without play. Since the selected setting of the individual components of the control system with respect to one another is not changed, a tilting will be almost impossible. As a result, the wear of the individual components is also reduced.
In a preferred embodiment, the devices for absorbing the centrifugal forces comprises a thrust bearing mounted between the control device and the control flap, particularly of a thrust ball bearing and a spring which, under prestress, continuously presses the portion of the control device which is to be supported against the thrust bearing. As a result of the thrust bearing, the friction between the control flap and the area to be supported is reduced to a minimum, whereby less energy for moving the control flap has to be applied by the actuator system. The thrust bearing is advantageously a thrust ball bearing, but any bearings can be used which reduce the friction between the components. At low centrifugal forces, the spring prevents a bearing play of the thrust bearing and protects against a displacement of the thrust bearing. Thus, also at low centrifugal forces, no bearing play will exist and a tilting will be prevented. The spring is preferably mounted around the bolt so that this bolt prevents a slipping of the spring.
The transmission of the movement of the control device to the flap is preferably implemented by means of a housing. By means of this housing, the linear movement is transmitted by way of roller bearings integrated therein to a bolt. The mounting of the bolt on the control flap will than cause a swivelling of the control flap.
The bolt is advantageously screwed into flap-side bearing eyes. This permits an easy mounting and, if required, an easy exchange. Naturally, in the event of circumstances caused by special stress which require a welding or gluing, this will also be possible.
In another preferred embodiment, the devices for absorbing the centrifugal forces consist of a roller bearing ball situated in the face of the bolt, and of a hollow socket interacting therewith and force-lockingly connected with the control flap. Thus, by way of the bolt by means of which the linking to the control flap is ensured, the control device is supported with respect to them. The point bearing of the ball in the hollow socket has a low frictional loss and by nature has no bearing play.
The radius of the hollow socket is preferably selected to be larger than the radius of the roller bearing ball, elliptical sections also being conceivable. This ensures a smooth-working point bearing which prevents a displacement of the control bar linkage in the span direction which, during the movement, converts little energy into friction and heat.
The hollow socket advantageously consists of synthetic sapphire, while the roller bearing ball consists of steel. Naturally, it is also possible to use a hollow socket made of a different bearing jewel, such as ruby. This material also does not bond with the roller bearing ball during friction.
The transmission of the movement of the control device to the flap is caused in another advantageous embodiment by way of two bolts on a fork, whereby the control axis is interrupted. In this case, the bolts are disposed in the control flap by way of roller bearings. As a result, a space is created between the flanks of the fork which can be utilized in the low height of the rotor blade. For example, a housing can be mounted in the space according to another embodiment, whereby the housing is provided for the conversion of the movement of the control device in one direction, while a fork can be used for the conversion of he movement of the control device into the other direction.
The bolts can be welded or glued to the fork. However, advantageously, the bolts are screwed to the fork. If required, this ensures an easy exchange of the stressed components without the requirement of high repair expenditures.
The roller bearings are preferably sealed off on the side which is outside in the span direction by means of asymmetrical radial packing rings. As a result, the mass of the charged roller bearing grease is held back by the projected surface of the seal.
The roller bearings are preferably needle roller bearings.
The bearing eyes accommodating the hollow socket and the bolts or roller bearings are inserts which can be slid in a form-locking manner into bores/openings of the control flap during the assembly, for which their outer contour must be adapted to the bores. By means of other inserts and check nuts, these inserts can be precisely fixed and positioned in the control flap, so that the play of all bearings is minimized. In addition, a simple exchange will be possible, as required.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.